This invention relates to an apparatus for accurately sewing together portions of knitted articles on a sewing machine.
The most widely used traditional method of joining together portions of knitted articles of manufacture is known to comprise a so-called "stitch linking" operation, wherein the loops of the edges to be joined in the knitwork are orderly slid, one at a time, over the impaling pins of a linking machine. After this orderly loading of the knitted stitches onto such pins is completed, they are caused to pass by a linking head whereat the stitch linking proper is carried out. The operation provides satisfactory results from an aesthetic and qualitative standpoint, but tends to slow down the whole process, owing additionally to and rather than the speed of the linking needles themselves, to the preliminary and basic operation of applying both articles or pieces to the needles, which operation has generally to be carried out by experienced and skilled personnel. All this brings about the inevitable consequence that where low cost products are aimed at, such a processing method ceases to be economically convenient.
Consequently, for low-cost articles, it has become common practice in the making up of knitwork (i.e., the application of borders for collars, strips, pockets, and other items of finish) to use conventional sewing machines. It will be understood that such machines allow for much higher production rates, with a lesser labor unit cost. On the other hand, this approach results in a far less accurate work, inferior both in quality and appearance; furthermore, the product is subjected to running of the loops since it is evident that the entirely random mode of sewing up the two knitted fabric edges, as performed by the sewing machine needle, leaves out several loops in the end courses of the joined pieces which constitute as many potential sources of running failure or ladders.
As regards the poorer quality of the articles obtained by processing them on a sewing machine, the following should be pointed out. Contrary to the linking machine, where it is provided for the linking to strictly occur at and along the selected course (or, more generally, the row of knitting) as a result of the item of manufacture being preset on the pins in the precise desired arrangement, on the sewing machine the parts to be joined are caused to move forward or advance by specially provided mechanical members of the machine (jaws, wheels, plates, and the like) in a manner that substantially deprives the operator of the possibility to direct the product as it passes under the sewing needle with an absolute and constant degree of accuracy. Now, whereas this inaccuracy may be of less importance in the case of some garments, there exist situations where a not so accurately controlled advance path, i.e., a zigzagging one to some extent (even though only between one course and an adjacent one) results in products of unacceptably poor quality. The instance may be quoted here of two patterned or rib stitch worked pieces that are to be sewn together, wherein perfect alignment and matching of the patterns in the two confronted pieces must be achieved.
Another limitation in the application of sewing machines for joining knitted items of manufacture resides (still by way of example) in the impossibility of joining to a flat stretched edge of one piece another piece which it is desired to keep slightly curled up at the very joining area: it will indeed appear that the operator has no means of controlling that the knitwork is kept curled in the amount and disposition as necessary to achieve the desired effect in the finished garment.
To sum it up, it may be stated that all the limitations cited and others yet, which are well known to the experts in the art, derive from the fact that, at the work area of the sewing machine needle, the item of manufacture is almost entirely, during the advance thereof, "dominated" by the driving mechanical action, thereby the only way in which the operator may control with sufficient (but incomplete) accuracy the stitch line of application would be that of making the work progress very slowly, in order to gain better control over the fabric movement. Such a remedy, however, opposes the basic reason why knitted garments are worked on sewing machines, that is the achievement of faster production rates, or faster sewing and advancing, as such a machine is capable of providing.